1. Field of the Invention
Exemplary aspects of the present invention relate to a transfer-fixing device, an image forming apparatus, and a transfer-fixing method, and more particularly, to a transfer-fixing device, an image forming apparatus, and a transfer-fixing method for transferring and fixing a toner image on a transfer material.
2. Description of the Related Art
A related-art image forming apparatus, such as a copier, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, forms a toner image on a transfer material (e.g., a sheet) according to image data by electrophotography. For example, a charger charges a surface of an image carrier. An optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data. A development device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the image carrier. The toner image is transferred from the image carrier onto a sheet via an intermediate transfer member. A fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image on the sheet. Thus, the toner image is formed on the sheet.
However, when a sheet having a rough surface is used, the intermediate transfer member may not fully conform to the surface of the sheet, and consequently a minute gap is formed between the intermediate transfer member and the sheet. As a result, abnormal electrical discharge occurs at the gap, and the toner image carried by the intermediate transfer member is not properly transferred to the sheet, resulting in a faulty image.
To address this problem, there are examples of a related-art image forming apparatus including a transfer-fixing device for performing a transfer process and a fixation process at the same time. Since the transfer-fixing device transfers a toner image to a sheet while applying heat to the toner image, heated toner particles are softened and melted into a viscoelastic block-like clot, and fixed to the sheet. Accordingly, even when a minute gap is formed between a sheet with a rough surface and a transfer-fixing member, the clotted toner is fixed into the gap, thereby forming a high-quality image.
However, since the transfer material (e.g., plain paper) has very small surface irregularities, when the image carrier contacts the transfer material, a surface of the image carrier including resin or rubber may not conform to such irregularities. Thus, a part of the toner image may fail to contact the transfer material.
FIG. 1 illustrates a transfer-fixing process in which a solid toner image is transferred from an image carrier to a transfer material and fixed thereon at a transfer-fixing nip in one example of the related-art image forming apparatus.
As illustrated in FIG. 1, after the solid toner image contacts the transfer material, the whole image may be transferred and fixed to the transfer material. Since the solid toner image has a continuous film-like shape, even when a part of the toner image does not contact the transfer material, the whole image may be successfully transferred and fixed to the transfer material.
FIGS. 2 and 3 illustrate a transfer-fixing process in which a dotted toner image is transferred and fixed to a transfer material. As illustrated in FIG. 2, when the toner image includes dots separated from each other, some dots fail to contact the transfer material and thus remain on the image carrier without being transferred to the transfer material, thereby causing an image defect. As illustrated in FIG. 3, even when the image carrier has a decreased hardness in order to conform more readily to the irregularities in a surface of the transfer material and the transfer material contacts the image carrier with an increased pressure, some dots still fail to contact the transfer material and remain on the image carrier. Thus, a complete image may not be transferred and fixed to the transfer material.
In such a transfer-fixing method, a sticking force of the toner particles causes the toner image carried by the image carrier to be transferred to the transfer material. Thus, if the toner particles fail to contact the transfer material, the toner image may not be transferred to the transfer material, thereby causing an image defect.
Additionally, such residual toner remaining on the image carrier may change from a liquid state to a solid state after passing through the transfer-fixing nip and may be fixed to the surface of the image carrier. Alternatively, the residual toner may adhere to other components contacting the image carrier or stick to other transfer material. As a result, wasted toner may cause environmental burdens, or may shorten a lifetime of a toner removal device.